s3:vfs: Correctly check if OFD locks should be enabled or not

s3:vfs: Correctly check if OFD locks should be enabled or not

Also the smb.conf options should only be checked once and a reload of
the config should not switch to a different locking mode.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=13770

Signed-off-by: Andreas Schneider <asn@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>
Autobuild-User(master): Jeremy Allison <jra@samba.org>
Autobuild-Date(master): Sat Feb  9 03:43:50 CET 2019 on sn-devel-144

(cherry picked from commit 7ff94b18e2e39567ef7a208084cc5c914c39d3bd)